Art of purifying yeast



Patented Feb. 25, 1936' i. I I

UNlTED STATES PATENT OFFICE No Drawing. Application April '4, 1929,Serial No. 352,586

Claims. (Cl. 19598) This invention relates to a process oi purifying(though the next step may be carried out without yeast producedpreferably by the fermentation of such separation) for instance, byoverflowing and, saccharine materials wherein either the yeast or ifdesired, greatly more diluted, so that the diluthe alcohol is the mainproduct. When such mation is from 1:6 upwardtd 1:10 or more, depend- 5terials have been fermented in refineries, brewing upon various factorssuch as material, etc

eries or distilleries or similar plants, the fermenter the variousrelations between the temperature at contains a sediment composedlargely of yeast, which the suspension is heated, the extent oi timewhich has been instrumental in producing the of the heating and theextent of the dilution all fermentation, and is healthy and vigorous,and have their eiiect on the suspension treated.

13 also contains a certain amount of alcohol and These relations mayfoe-determined by laboratory certain impurities of the fermentedmaterial. testings for any particular yeast sediment, an

This yeast may be coagulated and fiocculated may be charted andthe chartused in the comand then separatingly settled by asuitable methmercialoperation of my process. od such as gravitational sedimentation to sepa-This portion may be raised to a temperature rate out the portionscontaining the impure yeast that is much-higher, whereupon a thin darklayer M or the impurities.- The suspension i obtain is will separate outat the top of the liquid. This an aqueous suspension containingpractically. only is nearly all composed of a yeast of high proteinyeast of bright color having a high protein value, content but dark incolor, and hence not as dewhich may be treated, de-hydrated and dried,as sirable for sale for food purposes.

'20 herein described. This separation of the upper layer takes place mMy present process may be applied in the sep most advantageously at highdilution, heating or arating and settling steps inany process where.both, and each being a factor in the speed and a sediment containingyeast is treated by dilution, completeness of its formation, while alower di. heating and selective separation, or a combina lution andtemperature favors the precipitation tion of any of these steps. I ofthe lowermost layer containing the impurities, For my preferredprocedure, I then take the which portion may be sold for animal feed oryeast that may be removed irom its fermenters fertilizer. Asa series ofexamples, suppose the by any suitable means such as described in mydilution should be 1:1. 1,000 c. c. of, the sus= Patent No. 1,751,948with its'adulterant impuripenslonat the temperature of 15,

30 ties,'drawing ofi the clear liquid, and then washand C. would usuallyshow a very small seto ing out the sediment or drawing ofl the sediment'tlement after 1 hour, the rate decreasing graduand clear liquidsimultaneously when the fermenally and becoming nearly constant atthe'fith tatlon is completed, or the clear liquid may be hour, and aboutc. c., c. c., 200 c. c.,,

removed gradually and the yeast removed, using 245 c. c., and 250 c. c.;where the dilution is 1:2,

35 a Dorr thickener, then washing it and diluting the settlement in thfirst two hours proceeds to a concentration ofapproximately 1; 2. muchmore rapidly and where the dilution is 1:4

I may then settle out part of its impurities and usually the settlingtakes place very promptly dilute it to 1:4,and then heat it to a.temperature frequently more than half the suspension is somewhat above35 C. This temperature de-- cleared in the first hour, after which theclearing pends upon the concentration of the yeast. This of thesuspension progresses very slowly. As an 40,

will coagulate the yeast, but will not precipitate example, such asuspension containing 1000 c. c. it to a material extent, and will causea layer, may, at 10050. in the first fifteen minutes have chiefly ofimpurities, to fall" to the bottom .0! cleared its upper 650 c. c. inahalf hour; By sepathe settling tank; this layer is darker and thickrating out the dark upper layer, the'middle por and maycontainpart ofthe gums, cellulose, sand tion of the aqueous mixture, with only theliving 45 and most of the insoluble mineral salts, and per.- yeast ofhigh protein valueand light bright color haps some-yeast of low proteinvalue. suspended therein is left for further treatment.

This lower portion is only a small proportion While I have described aparticular modeof sepof the-suspension. It may be increased or dearatingthe yeast, I donot confine the application 50 creased amount to suit thevarious conditions of the below described method of'treatment to 50influencing the purity of the yeast, audit can be a yeast suspensionobtained as above described,

, dehydrated and dried, and sold for animal feed because the processbelow is applicable to a susor fertilizer. pension of yeast obtained byother methods, such The portion above-this layer may then be sep'- as,for instance, in the production of beer. 55 arated from the lower layerby suitable means .The treatment above described of selective 55 anysuitable method.

separation of the yeast is, of course, not to be confined to cases wherethree layers only appear; under many circumstances these layers may bemore numerous, and sometimes the limits of separation of layers may notbe sharply defined; it is convenient and substantially correct toconsider them as three. The cutting can be into more than threeportions.

Supposing, however, a suspension of clear yeast of high grade,practically freed from 1111-- purities has been obtained, thissuspension may be centrifuged and dried merely, but I prefer to treatthe yeast in it with chemicals that have no detrimental influence onliving beings, and have no fat solvent property nor destructive actionon the yeast cell, but arev used merely for the improvement of color. Ihave found this advantageous in getting a good light colored product.

A suitable chemical for this purpose, is acetic or phosphoric acid,hydrogen peroxide or weak alkali, also various inorganic salts such asbicarbonate of soda, sodium bisulphite. It is very important to choosethe chemicals very carefully, as quite often a dark color in the yeastis ,caused by the presence ,of inorganic salts, for

instance, iron salts. Insuch cases, an, alkali would precipitate them,and so would increase and not decrease any darkness in color of theyeast, either when treated or exposed to the air or. light. But a toodark color often arises from coloring matter, for instance, in themolasses and when so separated and washed, de-hydratedby any suitablemeans such as a centrifugal or filter press, and the wash water. may bereturned to a prior stage of the process.

The de-hydrated yeast which may have been centrifuged is dried. Thedrying may be done in any suitable dryer.

The dark yeast fromthe upper layer may be I similarly -treated,'v iz.centrifuged or dried, by

Where the liquid holding in suspension the yeast that would form boththe middle and upper layers is not allowed to settle until these layersseparate, the process of treating this liquid can follow the treatmentof the middle layer,

but usually the product is less desirable, and for reason the processcan be simplified when both layersare mingled together, and a less fineproduct obtained, but one more cheaply produced. Y

Yeast from the middle layer, refined as above,

is almost tasteless, has very light color and does not require anyfiller whatever, such as cellulose.

starch or ground cereal; while hitherto all pure dried yeast was eitherdarkin color or required fillers, the yeast obtained herebyisi light. Inthis process also, high temperaturesare avoided and the yeast cellstherefore are not ruptured, and, when molasses is used in thefermentation,

much of the calcium salt does not go into solution, as this salt is moresoluble in cold than in hot water, and this salt is collected in thelower layer.

Many variations may be made in the general method set forth above.Sometimes it is preferable to get one portion of the suspensioncontaining a particular level removed first, and then afterwardsseparate the other portions. This often makes the separation anddehydration easier.

The main purpose of using the wash waterthat had been used in a laterstage of the process in an earlier stage, or returning it to thefermenter or molasses mixer is chiefly the saving of alcohol. Any yeastcontained in the wash water is also returned.

It will be obvious from the foregoing that many changes may be madewithout departing from the spirit of my invention.

I claim:-'- I 1. In the art of purifying yeast wherein is containedlight colored and dark colored living yeast cells, the steps of forminga suspension of the yeast in water in which the proportion of. water isbetween one part yeast and four parts water and one part of yeast andten parts of water, then heating the suspension to substantially above35 C., until there forms at the top of the suspension a layer of darkcolored yeast, removing this layer and then decolorizing the yeast inthe remaining suspension by adding a member of the group composed ofacetic acid. phosphoric acid and hydrogen peroxide, and causing thesolution to stand until the yeast in said remaining suspension isdecolorized.

' 2. In the art of improving and lightening, the color of yeast in vasuspension of yeast discolorable by the presence of inorganic salts, thesteps of coagulating, fiocculating in an aqueous suspension, from whichthe insoluble impurities 'have been eliminated, and subsequently addingto the suspension, a chemical of the group composed of acetic andphosphoric acid and hydrogen peroxide, that will not combine with suchsaid inorganic salts that are, contained in the suspension.

3. In the art of improving the quality of yeast, in a suspension freedfrom insoluble impurities, said yeast being coagulated and flocculated,the

step of adding to the suspension a chemical of the group composed ofacetic and phosphoric acid and hydrogen peroxide.

4. Inthe art of improving the quality of yeast, in an aqueous suspensionfreed from impurities, said yeast'having been coagulated andflocculated, the steps of adding to the suspension a chemical of thegroup composed of acetic and phosphoric acid and hydrogen ,peroxide, andheating the suspension to,.a temperature suiiicient to precipitate andto settle anycalcium salt dissolved in the liquid of the suspension.

5. In the art of improving yeast, the step of"

